It is important in different locking constructions that the lock has distinct positions, locked and unlocked. There is a risk when unlocking a door, for instance during emergency evacuation of premises, that a door cannot be opened although it has been unlocked in the normal manner. In critical situations this may have disastrous results. Both security and fire-protection aspects must be respected. The locked position shall be firm and unlocking shall not be made more difficult, for instance when a crowd of people are pushing towards the exit, thereby unintentionally preventing its opening.